1. Field of Invention
The present invention relates to a ungrounded, reconfigurable, parallel mechanism based, force feedback exoskeleton device for the human ankle. The primary use for the device is aimed as a balance/proprioception trainer, while the exeskeleton device can also be employed to accommodate range of motion (RoM)/strengthening exercises. This device is also used for metatarsophalangeal joint exercises.
2. Background
The aim of the rehabilitation is to recover the patient's physical, sensory and neural capabilities that were impaired due to an illness or injury. Ankle rehabilitation is commonly necessitated after sprained ankles, one of the most common injuries in sports and daily life [1]. Losses of functional ability, ability to bear weight, and joint stability at the ankle are also experienced after neurological injuries secondary to stroke and contracture deformity secondary to cerebrovascular disease. Physiotherapy exercises are indispensable to re-gain range of motion (RoM) of the joint, to help restrengthen muscles to bear weight, to promote better awareness of joint position (proprioception), to ensure neural integrity, and to recover dynamic balance.
Rehabilitation of ankle injury is generally addressed in three sequential exercise phases [2], [3]. Exercises in the early phase focus on first enabling full RoM of the joint and then strengthening ankle muscles. Once the required RoM and flexibility is achieved and the muscles become strong enough to bear partial weight without inducing pain, the intermediate phase of therapy can be initiated, focusing on enhancement of proprioception ability through use of static balance exercises. In the final phase of the therapy, more advanced dynamic balancing exercises are practiced.
Traditional rehabilitation devices used to assist physiotherapy are simple passive equipment, such as elastic bands and ankle rehabilitation pumps for strengthening and stretching exercises; wobble boards and foam rollers for proprioception and balancing exercises. RoM exercises are generally performed manually by a therapist. Even though these types of equipment are simple and fixed-cost effective, these traditional devices fall short of collecting quantitative measurements of patient progress, monitoring patient history for re-evaluation, and achieving customized, interactive treatment protocols. The therapists are required to carry physical burden of movement therapy and to provide the patient with full attention while exercising with these devices.
Nowadays rehabilitation exercises have been done by the help of the robotic devices. Assistance of repetitive and physically involved rehabilitation exercises using robotic devices not only helps eliminate the physical burden of movement therapy for the therapists, but also decreases application related costs. Moreover, robot-mediated rehabilitation therapy allows quantitative measurements of patient progress and can be used to realize customized, interactive treatment protocols.
Beneficial effects of robot assisted rehabilitation protocols have been demonstrated over conventional therapy through clinical trials in the literature [4]. Recognizing the need for robot assisted rehabilitation devices for ankle physiotherapy, several designs have been proposed to date. Girone et al. proposed a force feedback interface, named Rutgers Ankle, based on Stewart platform [5]. A virtual reality based interactive training protocol was implemented using the Rutgers ankle for orthopedic rehabilitation [6]. The system was further studied through several case studies [7], [8]. Home-based remote ankle rehabilitation was addressed in Girone et al. [9], while in Boian et al, the system was extended to a dual Stewart platform configuration to be used for gait simulation and rehabilitation [10].
Dai et al. proposed another robotic device to treat sprained ankle injuries [11]. Unlike the Stewart platform design, this device progresses just enough degrees of freedom (DoF) to cover orientation workspace of the human ankle. The kinetostatic analysis presented in this reference emphasized the importance of employing a center strut to achieve higher stiffness from to device. Agrawal et al. proposed an ankle-foot orthosis for robot assisted rehabilitation and presented the kinematic analysis and the control of the proposed mechanism [12]. Similarly, Anklebot was proposed by Roy et al. to aid recovery of the ankle function [13]. This device can also be used to measure the ankle stiffness, which is a strong biomechanical factor for locomotion.
Syrseloudis and Emiris studied the translational and rotational RoM of the human ankle and foot through human subject experiments, and concluded that a parallel tripod mechanism with an additional rotational axis in series is the most relevant kinematic design to comply with human ankle related foot kinematics [14]. Yoon and Ryu proposed a hybrid four DoF parallel mechanism based footpad device and presented the kinematic analysis of the novel device [15]. This work was extended to allow for reconfiguration of the device to support several distinct exercise modes [3], [16].
It is thus an object of the invention to provide a device which has a reconfigurable design. Its implementation is simple and the device can be built assembling commercially available parts. Due to its reconfigurability, the device allows for both range of motion RoM/strengthening exercises and balance/proprioception exercises.